1. Field of the Invention
This invention relates to a thread cutting device for a cylinder bed forming seams machine for sewing by means of a plurality of needles on the pieces of fabric supported on a cylindrical bed while transporting the fabric pieces in a given direction.
Thread cutting devices of the type must have a thread cutter, and a thread catch member for catching needle thread loops formed in numbers corresponding to the number of needles and looper threads interlooped with the needle thread loops for directing them to the cutter. In cylinder bed sewing machines, however, the internal space of the bed is very limited and various components such as a looper and the like have to be housed in a limited internal space. For this reason, special consideration has been given with respect to the mounting position for the thread cutting device and the path of movement thereof.
A prior-art thread cutting device disclosed in U.S. Pat. No. 4,098,209 is shown in FIG. 10. In the FIG. 10 thread cutting device, a thread catch member 50 having dogleg-shaped slots 51, 51 is connected to a driving lever 52 so that when the lever 52 is pivotally moved from its position shown in the direction of arrow A, the thread catch member 50 is caused to move lower-leftwardly in FIG. 10 by the action of guide pins 53, 53 fitted in the slots 51, 51, being then allowed to move linearly in the leftward direction. A support member 55 having a slot 54 is urged leftward by a resilient member means 56, so that when the thread catch member 50 is moved lower-leftwardly, the support member 55 is actuated by the thread catch member 50 to move in the lower-leftward direction until it goes into abutment with a stopper 57. When the thread catch member 50 is in linear movement as aforesaid, the support member 55 is on standby as it is in abutment with the stopper 57, so that as the thread catch member 50 turns back with needle thread and looper thread (not shown) caught thereinto, the caught-up threads are cut by a thread cutter 58 provided at the front end of the support member 55.
As FIG. 12 illustrates, a straight line path X.sub.1 along which the thread catch member 50 is linearly moved is in orthogonal relation to the direction Y of fabric feed during sewing operation, and the starting point S of a path X.sub.2 which the thread catch member 50 follows when it is in lower-leftward movement is located away from an extension of the straight line path X.sub.1 so that the catch member 50 may not interfere with the movement of a looper 59 shown in FIG. 11.
The looper 59, as shown in FIG. 11, is caused to move toward and away from the straight line path X.sub.1 (see FIG. 12), along which the thread catch member 50 moves, while being inclined at an angle of .theta. relative to the path X.sub.1, and accordingly, when the movement of the looper 59 is stopped at a left dead point, the needle thread loops 60 are inclined at a specified angle relative to the direction Y of fabric movement.
Such a thread cutting device involves a problem that since it is simply of such arrangement that the thread catch member 50 is caused to move back and forth along the aforesaid straight line path X.sub.1, the catch member 50 may sometimes fail to catch some needle thread loop or loops 60 when it turns back on the straight line path X.sub.1, thus causing a loop catching error.